Developing a MVC Component/Adding verifications

From Joomla! Documentation

Why is the protected function _populateState() in the /admin/models/helloworld.php file? It doesn't appear in the original helloworld.php model file, and there isn't any indication as to the purpose of this function aside from the annotations within the function, which I don't fully understand.

Attention

Section about admin/views/helloworld/tmpl/edit.php is not the same as in file present in archive.

verification seems to operate even when required="false" is coded

I have expanded the helloworld component to have several other fields now, and set some of them to required="false" in the /models/forms/app.xml file. I still get "invalid field" when I leave the input box empty. Any ideas?

(later) I think I figured it out: the client-side script operates on every field it's assigned to, whereas the server-side may operate only on a field that's required and not empty. Not sure about that last, but I am sure that the client-side script operates, so you may want to code the regex differently in admin/models/forms/<com-name>.js (the client side) vs admin/models/rules/<field>.php .